Roll control system for a motor vehicle

ABSTRACT

A roll control system for installation between axially aligned wheels of a motor vehicle, the roll control system comprising a torsion bar; a first hydraulic actuator attached to one end of the torsion bar and attachable to one of the wheels; a second hydraulic actuator attached to the other end of the torsion bar and attachable to the other wheel; and an electronic control unit monitoring one or more predetermined vehicle operating conditions; wherein the first and second hydraulic actuators are substantially identical, each comprising a compression chamber containing hydraulic fluid, a rebound chamber containing hydraulic fluid, a movable piston between and fluidly isolating the compression chamber and the rebound chamber, a piston rod connected to the piston and extending through the rebound chamber, a gas chamber containing pressurised gas acting on the hydraulic fluid in the rebound chamber, and an electrically operated valve between the compression chamber and the rebound chamber and actuated by the control unit dependent on the monitored conditions, the valve being actuable between a two-way position in which the valve allows hydraulic fluid to flow between the compression chamber and the rebound chamber and a one-way position in which the valve allows hydraulic fluid to flow from the rebound chamber into the compression chamber but not from the compression chamber into the rebound chamber. Reduces the risk of incorrect latching of the torsion bar.

TECHNICAL FIELD

The present invention relates to a roll control system for a motor vehicle, and in particular to a semi-active roll control system.

BACKGROUND OF THE INVENTION

In order to prevent excessive rolling (which has an impact on vehicle attitude and handling) of a motor vehicle, especially during cornering, it is known to provide a torsion bar between the front wheels of a motor vehicle, and, in some cases, a second torsion bar between the rear wheels. However, during straight line motion of a vehicle and when the vehicle is off-road, the torsion bar can have a detrimental effect on comfort and wheel articulation. Semi-active roll control systems have been proposed which monitor various vehicle conditions. Such roll control systems include a locking device associated with the torsion bar and the wheels. When the sensed vehicle conditions indicate roll control is not required, the locking device is unlatched to effectively disconnect the effect of the torsion bar between the wheels. When the sensed vehicle conditions indicate that roll control is required, the locking device is latched to connect the wheels by way of the torsion bar. The latch position of the locking device determines the overall effect of the torsion bar on the wheels, and hence determines the level of roll control on the vehicle. In certain circumstances, it is possible to latch the torsion bar in the wrong position.

SUMMARY OF THE INVENTION

The object of the present invention is to lessen the risk and problems of potential incorrect latching.

A roll control system in accordance with the present invention for installation between axially aligned wheels of a motor vehicle comprises a torsion bar; a first hydraulic actuator attached to one end of the torsion bar and attachable to one of the wheels; a second hydraulic actuator attached to the other end of the torsion bar and attachable to the other wheel; and an electronic control unit monitoring one or more predetermined vehicle operating conditions; wherein the first and second hydraulic actuators are substantially identical, each comprising a compression chamber containing hydraulic fluid, a rebound chamber containing hydraulic fluid, a movable piston between and fluidly isolating the compression chamber and the rebound chamber, a piston rod connected to the piston and extending through the rebound chamber, a gas chamber containing pressurised gas acting on the hydraulic fluid in the rebound chamber, and an electrically operated valve between the compression chamber and the rebound chamber and actuated by the control unit dependent on the monitored conditions, the valve being actuable between a two-way position in which the valve allows hydraulic fluid to flow between the compression chamber and the rebound chamber and a one-way position in which the valve allows hydraulic fluid to flow from the rebound chamber into the compression chamber but not from the compression chamber into the rebound chamber.

In the present invention, the net force within each hydraulic actuator is such as to tend to move the piston in each hydraulic actuator to a full rebound position in which the volume of the associated rebound chamber is at a minimum. If the control unit actuates the valve of one of the hydraulic actuators for roll control, when the associated piston is not in the full rebound position, the net force will gradually move the piston towards full rebound. As a consequence, the roll control system of the present invention reduces the problem of latching the torsion bar in an incorrect position.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic view of a motor vehicle having a roll control system in accordance with the present invention;

FIG. 2 is a perspective view of the roll control system of FIG. 1;

FIG. 3 is a cross-sectional view of one of the hydraulic actuators of the roll control system of FIG. 2; and

FIG. 4 is a cross-sectional view of an alternative embodiment of hydraulic actuator for a roll control system in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows an outline of a motor vehicle 10 having a pair of front wheels 12 and a pair of rear wheels 14. Each wheel 12,14 is rotatably mounted on an axle 16 and attached to the body of the motor vehicle 10 by way of a suspension unit 18. A roll control system 20 in accordance with the present invention is connected between the front wheels 12. A substantially identical roll control system may be connected between the rear wheels 14, if desired.

Referring to FIG. 2, the roll control system 20 comprises a torsion bar 22, first and second hydraulic actuators 24, and an electronic control unit 26. The hydraulic actuators 24 are substantially identical. Each hydraulic actuator 24 is mounted between an end 28 of the torsion bar 22 and one of the suspension units 18. In general terms, and as shown in FIG. 3, each hydraulic actuator 24 comprises a compression chamber 30 containing hydraulic fluid, a rebound chamber 32 containing hydraulic fluid, a movable piston 34 between (and fluidly isolating) the compression chamber and the rebound chamber, a piston rod 58 connected to the piston and extending through the rebound chamber, an electrically actuated valve 36 between (and fluidly connecting) the compression chamber and the rebound chamber, and a compressible gas chamber 38 associated with the rebound chamber.

The position of each piston 34 is dependent on the position of the associated end 28 of the torsion bar 22 relative to the associated suspension unit 18. When the hydraulic actuator 24 is substantially in full rebound, the volume of the rebound chamber 32 is at a minimum. The desired position of each hydraulic actuator 24 during roll control is full rebound, when there is substantially no torque in the torsion bar 22.

The valve 36 is movable between a one-way position allowing fluid flow from the rebound chamber 32 into, but not out of, the compression chamber 30; and a two-way position allowing fluid flow in either direction between the compression chamber 30 and the rebound chamber 32. The valve 36 is preferably biased to the one-way position and is electrically connected to the control unit 26 by electrical leads 40.

The compressible gas chamber 38 contains a pressurised gas which acts on the hydraulic fluid in the rebound chamber 32. Due to the static pressure exerted by the pressurised gas in chamber 38, there is a net force exerted within the hydraulic actuator 24, which is proportional to the cross-sectional area of the piston rod 58 within the rebound chamber. The net force biases each hydraulic actuator 24 towards full rebound.

The control unit 26 is preferably a microprocessor which receives signals from one or more sensors (such as a vehicle speed sensor 42, a transmission speed sensor 44, a steering wheel angle sensor 46, and/or a driver preference switch 48) monitoring certain vehicle conditions and/or driver preference. The control unit 26 controls the movement of the valve 36 between the one-way position and the two-way position dependent on the signals received from the sensors, and may also actuate an alarm, such as a warning light 50, inside the vehicle 10 during certain monitored conditions.

When the control unit 26 determines that no roll control is required (typically during straight line motion of the vehicle 10 when off-road), the valves 36 are actuated to their two-way position such that hydraulic fluid can freely flow between the compression chamber 30 and the rebound chamber 32 in each hydraulic actuator 24. The pistons 34 are therefore free to float within each hydraulic actuator 24, and the torsion bar 22 is substantially disconnected from the front wheels 12.

When the control unit 26 determines that roll control is required, the valves 36 are moved to their one-way position to substantially prevent fluid flow from the compression chamber 30 to the rebound chamber 32 in each hydraulic actuator 24. The pistons 34 in each hydraulic actuator 24 are therefore effectively latched to prevent compression of the hydraulic actuators 24 due to the conditions sensed by the control unit 26. In this situation, the position of the torsion bar 22 relative to the front wheels 12 is effectively locked to provide the desired roll control for the vehicle 10. As mentioned above, the desired position for each hydraulic actuator 24 is full rebound. If, however, one of the pistons 34 is latched such that the associated hydraulic actuator 24 is not in full rebound, the torsion bar 22, the pressurised gas in chamber 38, and any road irregularities, will exert a net force on that piston. The effect of the net force is to push hydraulic fluid from the associated rebound chamber 32 into the associated compression chamber 30 by way of the valve 36 (which is set to allow fluid flow into, but not out of, the compression chamber). Such an arrangement allows the incorrectly latched piston 34 to gradually move to reduce the volume of the rebound chamber 32, and hence bring the hydraulic actuator 24 towards a full rebound position.

A preferred arrangement for each hydraulic actuator 24 is shown in FIG. 3. Each hydraulic actuator 24 comprises a tubular inner wall 52, and a tubular outer wall 54 substantially coaxial with the inner wall. The piston 34 makes a sealing sliding fit with the inner surface 56 of the inner wall 52. A piston rod guide 60 closes one end 62,64, respectively, of each of the inner wall 52 and the outer wall 54. The rebound chamber 32 is positioned within the inner wall 52 between the piston 34 and the piston rod guide 60. The piston rod 58 is secured to the piston 34, extends through the rebound chamber 32, makes a sealing sliding fit with the piston rod guide 60, and is secured to one end 28 of the torsion bar 22. The other end 66 of the outer wall 54 is closed and secured to the suspension unit 18. The other end 68 of the inner wall 52 is closed by the valve 36. The compression chamber 30 is positioned within the inner wall 52 between the piston 34 and the valve 36. A floating piston 70 makes a sealing sliding fit with the inner surface 72 of the outer wall 54 between the closed end 66 of the outer wall and the valve 36. The compressible gas chamber 38 is positioned between the floating piston 70 and the closed end 66 of the outer wall 54. The rebound chamber 32 is fluidly connected with the valve 36 and the floating piston 70 by way of apertures 74 in the inner wall 52 adjacent the piston rod guide 60, and the passage 76 between the inner wall and the outer wall 54.

Alternative arrangements for the above described arrangement for each hydraulic actuator 24 may be used. For example, the valve 36 may be positioned in the inner wall 52 rather than closing the other end 68 thereof, or even positioned in the piston 34. The mounting arrangement of the hydraulic actuator 24 may be reversed with the piston rod 58 attached to the suspension unit 18 and the outer wall 54 attached to the torsion bar 22. The compressible gas chamber 38 may be located at any other suitable positioned within the hydraulic actuator 24 but in connection with the rebound chamber 32.

An alternative embodiment of hydraulic actuator 24′ is shown in FIG. 4. In this alternative embodiment, like features have been given the same reference numeral, but primed (′), when compared to the embodiment of FIG. 3. The hydraulic actuator 24′ comprises a single tubular wall 53. The piston 34′ makes a sealing sliding fit with the inner surface 56′ of the wall 53. A piston rod guide 60′ closes one end 62′ of the wall 53. The rebound chamber 32′ is positioned within the wall 53 between the piston 34′ and the piston rod guide 60′. The piston rod 58′ is secured to the piston 34′, extends through the rebound chamber 32′, makes a sealing sliding fit with the piston rod guide 60′, and is secured to one end 28 of the torsion bar 22 (FIG. 2). The other end 66′ of the wall 53 is closed and secured to the suspension unit 18 (FIG. 2). The compression chamber 30′ is positioned within the wall 53 between the piston 34′ and the closed end 66′. The valve 36′ is mounted on, and extends through, the piston 34′ for controlled flow of hydraulic fluid between the rebound chamber 32′ and the compression chamber 30′. The electrical lead 40′ connecting the valve 36′ to the control unit 26 extends through an axially extending bore 55 in the piston rod 58′. An annular floating piston 70′ makes a sealing sliding fit with the piston rod 58′ and with the inner surface 72′ of a tubular sleeve 57 mounted on the valve 36′. The sleeve 57 is coaxial with the piston rod 58′ and positioned in the rebound chamber 32′. The sleeve 57 is spaced from the inner surface 56′ of the wall 53 to define a passage 59 within the rebound chamber 32′ for hydraulic fluid flow to the valve 36′. The compressible gas chamber 38′ is positioned inside the sleeve 57 between the floating piston 70′ and the valve 36′. The rebound chamber 32′ is therefore fluidly connected with the valve 36′ and the floating piston 70′. An outer sleeve 61 and a compression stop member 63 may be mounted on the piston rod 58′ outside of the rebound chamber 32′ to provide protection for the piston rod guide 60′. A stop member 65 may be mounted on the piston rod 58′ inside the rebound chamber 32′ to ensure that the floating piston 70′ is retained inside the sleeve 57.

The operation of the hydraulic actuator 24′ is substantially the same as the operation described above for the hydraulic actuators 24 shown in FIGS. 2 and 3. If the piston 34′ is latched in any position other than full rebound, a net force is exerted on the piston to push hydraulic fluid from the rebound chamber 32′ into the compression chamber 30′ by way of the valve 36′ (which is set to allow fluid flow into, but not out of, the compression chamber). As an alternative, the mounting arrangement of the hydraulic actuator 24′ may be reversed with the piston rod 58′ attached to the suspension unit 18 and the wall 53 attached to the torsion bar 22. As a further alternative, the gas chamber 38′ and floating piston 70′ may be positioned elsewhere in the rebound chamber 32′.

The present invention provides a roll control system 20 in which the hydraulic actuators 24,24′ reduce problems associated with latching of the torsion bar 22 in the wrong position. Also, the hydraulic actuators 24,24′ are self-contained hydraulic units and do not require external hydraulic connections, which allows easier installation of the roll control system 20 in the vehicle 10. 

What is claimed is:
 1. A roll control system for installation between axially aligned wheels of a motor vehicle, the roll control system comprising a torsion bar; a first hydraulic actuator attached to one end of the torsion bar and attachable to one of the wheels; a second hydraulic actuator attached to the other end of the torsion bar and attachable to the other wheel; and an electronic control unit monitoring one or more predetermined vehicle operating conditions; wherein the first and second hydraulic actuators are substantially identical, each comprising a compression chamber containing hydraulic fluid, a rebound chamber containing hydraulic fluid, a movable piston between and fluidly isolating the compression chamber and the rebound chamber, a piston rod connected to the piston and extending through the rebound chamber, a gas chamber containing pressurised gas acting on the hydraulic fluid in the rebound chamber, and an electrically operated valve between the compression chamber and the rebound chamber and actuated by the control unit dependent on the monitored conditions, the valve being actuable between a two-way position in which the valve allows hydraulic fluid to flow between the compression chamber and the rebound chamber and a one-way position in which the valve allows hydraulic fluid to flow from the rebound chamber into the compression chamber but not from the compression chamber into the rebound chamber.
 2. A roll control system as claimed in claim 1, wherein the valve of each hydraulic actuator is biased to the one-way position.
 3. A roll control system as claimed in claim 1 or claim 2, wherein each hydraulic actuator has a tubular inner wall and a tubular outer wall coaxial with the inner wall, the piston making a sealing sliding fit with the inner surface of the inner wall to define the compression chamber and the rebound chamber within the inner wall, a passage being formed between the inner wall and the outer wall for the flow of hydraulic fluid from the rebound chamber to the compression chamber.
 4. A roll control system as claimed in claim 3, wherein one end of the inner wall and one end of the outer wall are closed by a piston rod guide through which the piston rod extends in a sealing sliding fit.
 5. A roll control system as claimed in claim 4, wherein the valve is positioned at the other end of the inner wall.
 6. A roll control system as claimed in claim 4, wherein the gas chamber is positioned at the other end of the outer wall and is defined by a floating piston which makes a sealing sliding fit with the inner surface of the outer wall.
 7. A roll control system as claimed in claim 1 or claim 2, wherein each hydraulic actuator has a tubular wall, the piston making a sealing sliding fit with the inner surface of the wall to define the compression chamber and the rebound chamber within the wall, and wherein the valve is mounted on, and extends through, the piston.
 8. A roll control system as claimed in claim 7, wherein the gas chamber is positioned inside the rebound chamber and is defined by a tubular sleeve mounted in the valve coaxial with the piston rod, and by an annular floating piston which makes a sealing sliding fit with the piston rod and with the inner surface of the sleeve.
 9. A roll control system as claimed in claim 1, wherein the control unit is a microprocessor which is electrically connected to one or more sensors mountable in the motor vehicle for monitoring the one or more predetermined vehicle operating conditions.
 10. A roll control system as claimed in claim 1, wherein the one end of the torsion bar is attached to the piston rod of the first hydraulic actuator, and the other end of the torsion bar is attached to the piston rod of the second hydraulic actuator.
 11. A roll control system as claimed in claim 2, wherein the one end of the torsion bar is attached to the piston rod of the first hydraulic actuator, and the other end of the torsion bar is attached to the piston rod of the second hydraulic actuator.
 12. A roll control system as claimed in claim 3, wherein the one end of the torsion bar is attached to the piston rod of the first hydraulic actuator, and the other end of the torsion bar is attached to the piston rod of the second hydraulic actuator.
 13. A roll control system as claimed in claim 7, wherein the one end of the torsion bar is attached to the piston rod of the first hydraulic actuator, and the other end of the torsion bar is attached to the piston rod of the second hydraulic actuator.
 14. A roll control system as claimed in claim 5, wherein the gas chamber is positioned at the other end of the outer wall and is defined by a floating piston which makes a sealing sliding fit with the inner surface of the outer wall. 